Process for producing metallic film resistors

ABSTRACT

A PROCESS FOR PRODUCING METALLIC FILM RESISTORS, COMPRISING FORMING TWO OR MORE LAYERS OF DIFFERENT METALS ON THE SURFACE OF HEAT-RESISTANT INSULATING SUBSTRATES ONE ON THE OTHER BY NON-ELECTROLYTIC PLATING OR ELECTROPLATING AND THEREAFTER SUBJECTING THE COATED SUBSTRATES TO HEAT TREATMENT, WHEREBY THE DIFFERENT METALS ARE ALLOYED BY INTERLAYER DIFFUSION AND THUS A METAL ALLOY COATING IS FORMED ON THE SURFACE OF THE INSULATINGSUBSTRATES.

NOV. 23, 1971 TAKESHl s w E'I'AL 3,621,561

PROCESS FOR PRODUCING METALLIC FILM RESISTORS Filed Dec. 24, 1968 3Sheets-Shoot 1 2 FIG. w

3 FIG. /c 2 5 4 3 FIG. la 2 I 6 w F/G. /a d Nov. 23, 1971 TAKESHIHASEGAWA ErAL 3,621,567

PROCESS FOR PRODUCING METALLIC FILM RESISTORS Filed Dec. 24, 1968 3Sheets-Sheet a 9 it a 2000- S 3% E 2 ,5/000 3 g u 2Q 40 60 80 N/WE/GHTPERCENT 6 P76. 3 -45 4000- 40 :i k ,gaooo- JOE Q -25 $2609- g ggr40 TEMPE/mm mm? g k coa F/c/EA/r moo -/0 [3 i f 0 400 5390 HEATTREAWE/VT /000 TEMPERATURE?) United States Patent 3,621,567 PROCESS FORPRODUCING METALLIC FILM RESISTORS Takeshi Hasegawa, Neyagawa-shi, andYasuhiro Shindo,

0saka,'Japan, assignors to Matsushita Electric Industrial Co., Ltd.,Osaka, Japan 7 Filed Dec. 24, 1968, Ser. No. 786,637

Int. Cl. H01c 7/00, 17/00 us; or. 29-620 2 Claims ABSTRACT OF THEDISCLOSURE This invention relates in general to a process for producingmetallic film resistors, and more particularly to a process forproducing metallic film resistors which comprises forming layers ofdifferent metals on the surface of heat-resistant insulating substratesone on the other by plating and subjecting the coated substrates to heattreatment to effect interlayer diffusion of the metals, whereby an alloycoating is formed on the surface of the substrates.

In the production of metallic film resistors, two methods are beingemployed at present, i.e. vacuum evaporation coating and sputtering.Vacuum evaporation coating is a method of depositing a metal on thesurface of an insulating substrate by placing said substrate in a vacuumof the order of 10- to 10'" mm. Hg wherein the metal is evaporated at anelevated temperature. However, since the operation has to be carried outin vacuum, thismethod has the disadvantages of requiring an apparatuswhich is complicated in structure and diflicult to handle, being lowin'productivity and raising the cost of the product. Furthermore,according to this method it is difficult to control the compositionratio of component -iletals in the vacuum evaporation of an alloy ofsaid metals. On the other hand, sputtering is a method of depositing ametal on the surface of an insulating substrate in vacuum by placing thesubstrate in front of a positive electrode and impressing a voltage ofthe order of 1000 to 1500 v. across said metal, which constitutes anegative electrode, and said positive electrode. This method like vacuumevaporation coating has also to be carried out in vacuum, and thereforehas the drawbacks of requiring a complicated apparatus, being low inproductivity and raising the cost of the product resistor.

The present invention has for its object the provision of a process forproducing metallic film resistors, which comprises coating the surfaceof a heat-resistant insulating substrate with a layer of chemicalplating, forming la'yers of 'electroplatings on said layer of chemicalplating in superposed relation and thereafter subjecting the coatedsubstrate to heat treatment in a non-oxidizing atmosphere, whereby analloy coating is formed on said substrate uponinterlayer diffusion.

The present invention will now be described in detail in conjunctionwith the accompanying drawings, in which:

FIGS. 1a to 1e are views illustrating in sequence the steps of theprocess for producing metallic film resistors according to the presentinvention;

FIG. 2 is a characteristic diagram according to the first embodiment ofthe invention;

FIG. 3 is a characteristic diagram according to the second embodiment ofthe invention;

FIG. 4 is a characteristic diagram according to the third I embodimentof the invention; and

FIG. 5 is a characteristic diagram according to the fourth embodiment ofthe invention.

The process of the instant invention will be described with reference toFIGS. 1a to la in sequence. FIG. la

shows a heat-resistant insulating substrate and FIG. 1b.

shows the substrate 1 of FIG. 1 after the surface thereof has beensubjected to etching with hydrogen fluoride to facilitate bonding of acoating thereto. Numeral 2 designates the heat-resistant insulatingsubstrate thus treated.

FIG. 10 is a chemical plating step in which a layer of chemical plating3 of copper or nickel is formed on the surface of the heat-resistantinsulating substrate 2 of FIG. 2 in a thickness of 0.4 to 0.5 FIG. 1d isan electroplating step in which a layer of electroplating 4 of copper ornickel is formed on the surface of the chemical plating 3, formed on thesubstrate 2 in the step of FIG. 10, in a thickness not greater than 2,uand further a layer of electroplating 5 of a metal different from thatof the layer of electroplating 4, e.g. nickel, copper or zinc, is formedon top of said electroplating layer 4 in a thickness not greater than2,17. Where a coating of greater thickness or a coating of an alloy ofthree or more different metals is required, this may be attained byforming a multiplicity of plating layers, each having a thickness of 2aor smaller, alternately one on top of another. FIG. 1e is aheat-treatment step in which the coated substrate of FIG. 1d issubjected to heat treatment in a non-oxidizing atmosphere for apredetermined period at a temperature of 400 C. or higher to effectinterlayer diffusion and thereby to form an alloy coating. The productthus obtained is used as an electric resistor or a heating element.

EXAMPLE 1 A 3.5 thick chemical plating layer of nickel was formed on thesurface of porcelain rods having a diameter of 3 mm. and a length of 11mm. and on top of the nickel plating layer was further formed anelectroplating layer of copper. The thickness of the copper platinglayers on the respective substrate porcelain rods was varied byadjusting the current conducted, such that the per- 1 copper-nickelalloy coating was produced on the respective substrates. The temperaturecoeflicients of the respective finished resistors were measured, theresults of which are shown in FIG. 2.

EXAMPLE 2 A 0.4 to 0.5 thick chemical plating layer of copper was formedon the surface of porcelain rods having a diameter of 3 mm. and a lengthof 11 mm. and on top of the copper plating layer were formed 1 thickelectroplating layers of copper and 1, thick electroplating layers ofnickel alternately, the total thickness of the cop per electroplatinglayers and the total thickness of the nickel electroplating layers being5 respectively and the total thickness of the electroplating layersbeing 10 The resistors thus produced were subjected to heat treatment ina 10% hydrogen-containing nitrogen atmosphere each for 2 hours at 200 to1000 C. The temperature coefficients and the sheet resistances of therespective finished resistors were measured with the results as shown inFIG. 3. From the electron microscopic photos and the analysis by X-raydiffraction, it was COnfirrned that diffusion begins abruptlyat 400 to600 C. and the metals are alloyed completely at 800 C.

EXAMPLE 3 A 0.4 to 0.5 .0 thick chemical plating layer of copper wasformed on the surface of porcelain rods having a diameter of 3 mm. and alength of 11 mm. and on top of the copper plating layer were formedelectroplating layers of copper and nickel alternately such that thetotal thickness of said electroplating layers becomes 11p. and thepercentage by weight of the nickel varies in the range from to 100% (acoating of 100% by weight of nickel was obtained by using nickel for thechemical plating layer and forming an electroplating layer of nickel ontop of the chemical plating layer or nickel). The respective materialresistors thus produced were subjected to a heat treatment in a 10%hydrogen-containing nitrogen atmosphere for 2 hours at 800 C., whereby acoppernickel alloy coating was formed on each substrate porcelain rod.The temperature coefiicients and the sheet resistances of the finishedresistors were measured with the results as shown in FIG. 4.

EXAMPLE 4 A 0.4 to 0.5 thick chemical plating layer of copper was formedon the surface of porcelain rods having a diameter of 4.5 mm. and alength of 14 mm. and on top of the copper plating layer were formed a1;]. thick electroplating layer of nickel and a 1 thick electroplatinglayer of zinc in the order mentioned. The resistors thus produced weresubjected to heat treatment in a 10% hydrogen-containing nitrogenatmosphere for 1 hour at prescribed temperatures ranging from normaltemperature to 700 C. The temperature coefficients and the sheetresistances of the respective finished resistors were measured with theresults as shown in FIG. 5.

EXAMPLE TABLE 1.-TEST RESULTS Type Tests 2 w., 51 ohms 5 w., 160 ohmsTemperature coefficient (p.p.m./ 0.)... +60 +40 Short-time overload(percent) +0.03 0. 017 Humidity (percent) +0. 18 -0. 029 Load life(percent) +0. 74 +0. 007 Life in humidity (percent) +0.23 +0. 42Soldering effect (percent).- +0.02 0. 016 Shelf life (percent) +0. 0015:0

Testing conditions (1) Temperature coefficient.-The temperaturecoefficients were measured in a temperature range from 30 to +180 C.

(2) Short-time overload.A voltage 2.5 times the rated voltage wasimpressed for 5 seconds.

(3) Humidity.The resistor units were left to stand in a space at anambient temperature of 40 C. and a humidity of to (90 to 95 RH.) for 240hours with no load connected thereto.

(4) Load life.-A cycle of impressing the rated voltage for 1.5 hours andinterrupting the voltage for 0.5 hour was repeated for 1000 hours at anambient temperature of 40 C.

(5) Life in humidity.A cycle of impressing the rated voltage for 1.5hours and interrupting the voltage for 0.5 hour was repeated for 1000hours in a space at an ambient temperature of 40 C. and a humidity of 90to 95%.

(6) Soldering effect.A lead wire (resistor terminal) was immersed in asolder at 350 C. for 3 seconds.

(7) Shelf life-The resistor units were left to stand in a space at roomtemperature and normal humidity for 1 year with no load connectedthereto.

According to the vacuum evaporation coating and the sputtering whichhave been employed heretofore in the production of metallic filmresistors, the operations must be carried out in vacuum and, therefore,the apparatus used becomes complicated and the composition ratio of analloy coating to be formed can hardly be controlled, with theaccompanying results that the productivity of the methods is low andthat the cost of the finished resistors becomes high, as statedpreviously.

On the contrary, the process of this invention wherein use is made ofthe chemical plating and electroplating techniques, can be performed atnormal temperature and normal pressure. Therefore, the apparatus usedcan be simplified; the thickness and the composition of the coating canbe easily controlled; the productivity can be enhanced and the costofthe product can be reduced. Furthermore, although wire wound resistorsare predominantly being used at present as resistors of low resistancevalue, it is possible according to the process of this invention toproduce film resistors whose resistance value is in the same range asthe wire wound resistors. It is also to be noted that since the platingtechniques are used in the process of this invention, the shape of aresistor produced can be selected freely and the temperature coefficientof the resistor can also be selected freely in the range from to +3500p.p.m./ C. by changing the composition ratio of the metals used.Therefore, this invention is of great industrial advantage over theprior art.

We claim:

1. A process for producing metallic film resistors comprising: forming alayer of copper chemical plating on a heat-resistant insulatingsubstrate; forming alternating layers of copper and nickelelectroplating, starting with the copper layer on top of said layer ofcopper chemical plating; and thereafter heating the plated substrate ina non-oxidizing atmosphere to cause diffusion between discrete layers ofplating, thereby obtaining an alloy coating resistor film.

2. A process for producing metallic film resistors comprising: forming alayer of copper chemical plating on a heat-resistant insulatingsubstrate; forming alternating layers of nickel and copperelectroplating, starting with the nickel layer on top of said layer ofcopper chemical plating; and thereafter heating the plated substrate ina non-oxidizing atmosphere to cause diffusion between discrete layers ofplating, thereby obtaining an alloy coating resistor film.

References Cited (Other references on following page) Maissel 117-217 5UNITED STATES PATENTS Maissel et a1 29-610 X Schneble, Jr., et a1.117-217 X Loeb et a1 29-620 UX Knutson 29-620 5 Slay, Jr., et a1 117-217X Solberg et a1 29-620 Jones et a1. 117-217 6 FOREIGN PATENTS 1,067,4752/1965 Great Britain 338-308 JOHN F. CAMPBELL, Primary Examiner R. J.SHORE, Assistant Examiner U.S. Cl. X.R. 117-217; 338-308

